Chemometrics is the science of relating measurements made on a chemical system or process to the state of the system via application of mathematical or statistical methods. It is many times used to predict the properties, such as chemical composition, of structures based on their spectral response.
The advantage of chemometric-based solutions is that they can be faster and more generally applicable than other approaches, such as direct chemical sampling. This is especially true in medical applications. One example is blood glucose monitoring, as commonly performed by diabetics. The spectroscopic transdermal chemometric assessment of blood glucose levels has been proposed as an alternative to the painful blood sampling that must be performed many times per day, in some cases.
Another application concerns the assessment of the state of blood vessel walls such as required in the diagnosis of atherosclerosis. This is an arterial disorder involving the intimae of medium- or large-sized arteries, including the aortic, carotid, coronary, and cerebral arteries. Atherosclerotic lesions or plaques can contain complex tissue matrices, including collagen, elastin, proteoglycans, and extracellular and intracellular lipids with foamy macrophages and smooth muscle cells. In addition, inflammatory cellular components (e.g., T lymphocytes, macrophages, and some basophiles) can also be found in these plaques.
Disruption or rupture of atherosclerotic plaques appears to be the major cause of heart attacks and strokes, because, after the plaques rupture, local obstructive thromboses form within the blood vessels.
Although the risk of plaque rupture usually cannot be predicted, many postmortem examinations have revealed that this risk depends mainly on plaque composition. Most ruptured atherosclerotic plaques are characterized structurally by the formation of a large, soft, lipid-rich, necrotic core covered by a thin fibrous cap, densely infiltrated by macrophages. Of these features, lipid accumulation in so-called “lipid pools” is the most frequently observed precondition for rupture. Inflammation is also a major feature of nonruptured, but eroded, thrombosed plaques.
Near infrared (NIR) spectroscopy can be used to measure and mathematical, including statistical, techniques applied to extract information from the lower resolution NIR spectral data. Mathematical manipulations such as linear regression of the spectral band of interest and classic least squares and inverse least squares and other multivariate analysis tools are available for building quantitative calibrations as well as qualitative models for discriminant analysis.